Currently, with respect to a fluid flow sensor used in an air flow meter which is provided in an electronic controlled fuel injection apparatus for an internal combustion engine of an automobile or the like to measure an intake air amount, those of a thermal type can directly detect a mass air flow and are being mainly used.
Of these, especially a thermal type air flow sensor element produced by an MEMS (Micro Electro Mechanical Systems) technique using a semiconductor can reduce the cost and can be driven by a low electric power, and hence has attracted attention.
In such a sensor using an MEMS, the sensor assembled on an expensive metal or a ceramic substrate is subjected to resin encapsulation to achieve cost reduction and miniaturization. In this connection, resin encapsulation has been proposed in which a mold resin having an opening formed only at a position for a sensor element portion for measurement is used and a portion of the sensor except the sensor element portion is encapsulated by the mold resin.
As an example of a conventional resin encapsulation technique having an opening in a part of the resin, PTL 1 has a description of a technique in which a mold having a protruding portion and a lead frame having fitted thereto a semiconductor element are meshed to form a depressed groove portion between a detector unit and an electrode unit of the semiconductor element. In PTL 1, a mold resin is introduced into the depressed groove portion to obtain an anchoring effect, so that the bond strength of the mold resin to the surface of the semiconductor element is improved, preventing the occurrence of peeling or the formation of cracks in the mold resin layer around the opening.
Further, PTL 2 has a description of a technique in which a buffer layer is formed in a region in contact with a housing present in the outer periphery of an opening. The buffer layer has a function of preventing the mold for forming an opening from breaking the detector unit, and a function as a stress relaxation layer between an integrated circuit and a semiconductor electronic element. The buffer layer is formed from a resin material, such as an epoxy resin, or an organic material, such as a silicone rubber.